Field of the Invention
The present invention relates to zoom lenses and an image pickup apparatus including the zoom lenses, and particularly, is suitable for a broadcasting TV camera, a cinema camera, a video camera, a digital still camera and a silver-halide film camera.
Description of the Related Art
In recent years, zoom lenses with a high zoom ratio and high optical performance are demanded for an image pickup apparatus, such as a TV camera, a cinema camera, a film camera and a video camera. Particularly, to handle various photographic scenes, a wide focal length range is desired for zoom lenses attached to a TV camera or a cinema camera as a professional video imaging system.
An example of a method of increasing the zoom ratio includes a method of displacing the focal length range of the zoom lenses. To realize this, proposed systems further include magnification-varying groups in a relay unit of the zoom lenses.
For example, Japanese Patent Application Laid-Open No. S49-66354 discloses zoom lenses including, from an object side to an image side, a positive first lens unit, a negative second lens unit, a negative third lens unit, a positive fourth lens unit, a negative fifth lens unit, a negative sixth lens unit and a positive seventh lens unit. The second lens unit and the third lens unit both serving as a first magnification-varying group move. The fifth lens unit and the sixth lens unit both serving as a second magnification-varying group move. Japanese Patent Application Laid-Open No. H03-161729 discloses zoom lenses including, from the object side to the image side, a focusing lens unit, a zooming lens unit and a relay lens unit, wherein the relay lens unit includes, from the object side to the image side, three lens units having a positive refractive power, a negative refractive power and a positive refractive power. The zooming lens unit moves in a first magnification-varying group. In a second magnification-varying group, the lens unit having a negative refractive power in the relay lens unit moves on an optical axis, between two positions that are the same image plane position.
Positive-lead type zoom lenses are known as zoom lenses with a high aperture ratio and high zoom ratio, the zoom lenses including, from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power for varying magnification, a third lens unit having a positive refractive power for varying magnification, and a fourth lens unit having a positive refractive power. A convergent ray enters the fourth lens unit in the zoom lenses.
A case in which the fourth lens unit further includes magnification-varying groups to displace the focal length range of the zoom lenses will be described.
In Japanese Patent Application Laid-Open No. S49-66354 and Japanese Patent Application Laid-Open No. H03-161729, a lens unit (first sub lens unit) on the image side next to the lens unit that moves when the first magnification-varying group changes the magnification has a positive refractive power. When the first sub lens unit having a positive refractive power is provided to the fourth lens unit of the positive-lead type zoom lenses as in Japanese Patent Application Laid-Open No. S49-66354 and Japanese Patent Application Laid-Open No. H03-161729, the degree of convergence of a ray incident on a lens unit (second sub lens unit) that moves when the second magnification-varying group changes the magnification is high. As a result, the refractive power of the second sub lens unit needs to be strong to displace the focal length range of the zoom lenses toward the long focal length side based on the movement of the second sub lens unit, and it is difficult to realize high optical performance. The negative refractive power of the second sub lens unit is strong, and the lens diameter of the lens unit on the image side of the second sub lens unit increases.